docs: fix math stuff in chemkin docstrings.
docs: fix math stuff in chemkin docstrings.

note the r""" at the start so that the slashes don't all
need to be escaped like \\so

nickvandewiele/RMG-Py,nyee/RMG-Py,chatelak/RMG-Py,pierrelb/RMG-Py,chatelak/RMG-Py,nickvandewiele/RMG-Py,nyee/RMG-Py,pierrelb/RMG-Py